Unveiling the Potential of Strain-Engineered Zinc-Blende ZnTe for Solar Energy Conversion: First-Principles Insights into Structural Stability, Optoelectronic Properties, and Photocatalytic Performance

The escalating demand for clean energy and environmental remediation has intensified research into advanced photocatalytic and photovoltaic materials capable of harvesting solar energy efficiently, thereby supporting renewable energy technologies and the transition toward a low-carbon future. Among these materials, zinc-blende (ZB) ZnTe is a promising II–VI semiconductor owing to its direct band gap of approximately 2.291 eV. However, its relatively wide band gap limits its ability to harness a broader portion of the solar spectrum. In this study, first-principles calculations were performed using the WIEN2k package and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential to systematically investigate the effects of isotropic tensile strain (0–5%) on the structural, mechanical, dynamical, electronic, optical, photovoltaic, and photocatalytic properties of ZnTe. The stability of ZB ZnTe was evaluated using formation energy calculations, elastic constant analysis, and phonon dispersion analysis, confirming its thermodynamic, mechanical, and dynamical stability across the studied strain range. All strained structures retain a direct band gap, which decreases progressively from 2.291 eV in the unstrained state to 1.712 eV at 5% tensile strain, demonstrating effective modulation of the electronic structure through strain engineering. This reduction is accompanied by enhanced optical absorption and optical conductivity in the visible region, indicating improved light-harvesting potential. Consequently, the photovoltaic performance, assessed using the spectroscopic limited maximum efficiency (SLME) model, improved substantially, with the SLME increasing from 16.71% in the unstrained structure to 28.83% at 5% tensile strain. Under acidic conditions, the band-edge positions meet the thermodynamic requirements for overall water splitting and CO2 reduction throughout the investigated strain range, while the theoretical solar-to-hydrogen (STH) efficiency increases from 7.09% in the unstrained structure to 12.08% at 5% tensile strain. This improvement is accompanied by a narrowing of the pH range suitable for photocatalytic reactions. Regarding pollutant degradation, the thermodynamic favorability of •O2− generation is maintained at all strain levels, whereas •OH generation becomes unfavorable under tensile strain, indicating that •O2− is likely to be the predominant reactive oxygen species. Although the limited availability of •OH may constrain the complete mineralization of recalcitrant organic pollutants, further oxidation through alternative reaction pathways may still enable their conversion into CO2, H2O, and inorganic ions. This study establishes tensile strain engineering as a theoretical strategy for tailoring the optoelectronic properties of ZnTe for photovoltaic and multifunctional photocatalytic applications, providing insights into its potential for advancing next-generation solar energy conversion and environmental remediation technologies.